[Stk] SKINI AfterTouch & ChannelPressure

[Perry R Cook]

Carlos,

Different interpretations of the MIDI spec call these two
things differently.

But the basic idea is that there is Channel Pressure,
often called After Touch, which affects all notes
currently sounding on that channel.
Almost every MIDI keyboard that has After Touch
implements this, because it's cheaper than Poly.
AfterTouch is most often taken to mean Channel
Pressure, hence the overloading in SKINI.

Poly Pressure, sometimes called Polyphonic AfterTouch,
allows aftertouch to be sensed and sent from each individual
key on a keyboard.  So if I'm sounding a C major chord
and press on the E, only the currently sounding E would
be affected.  Very few synthesizers and controllers
implement poly pressure, but some do.  In STK it's called
PolyPressure.

The extra alias of AfterTouch into Controller 128 (not a
legal MIDI controller number, but a legal SKINI controller
number) was a hack so that the .tcl scripts could use the
same ControlChange function for all sliders.  It's a hack.

PRC

On Mon, 9 May 2005, Carlos Pita wrote:

> Hi! I can't make sense of the following equalities
> (left side taken from MIDI specification at
> http://www.borg.com/~jglatt/tech/midispec.htm,
> right side from SKINI.msg):
>
> 0xa0 (AfterTouch) == 160 == __SK_PolyPressure_
> 0xd0 (ChannelPressure) == 208 == __SK_AfterTouch_ == __SK_ChannelPressure_
>
> Why are you treating AfterTouch (individual key pressure)
> and ChannelPressure (average channel pressure) as the same
> thing and mapping them to MIDI ChannelPressure? And
> what do you mean by PolyPressure and why is it mapped
> to AfterTouch?
> Is the rationale that PolyPressure gives the individual
> key pressure while AfterTouch aka ChannelPressure should
> be considered per channel pressure? If it is this way,
> I find it very confusing, as it not only renames MIDI
> messages but also refers to a different thing than MIDI by
> AfterTouch.
> Then there is AfterTouch_Cont, that is, AfterTouch
> seen as a control. What is the role of AfterTouch here:
> x key or x channel? What is the point of having it
> again as a control (I noted that instruments in the
> stk distribution prefer AfterTouch_Cont control over
> AfterTouch message) ?
>
> Thank you in advance.
> Regards,
> Carlos
>
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